372 DOLPHINS can leap right out of the water, and while in the air can turn its head from side to side, a capability which has not been mentioned in any other Whale. It can also stay under water for an unusually long period. Captain Gray,1 who has made an accurate study of this species, states that so long a period as two hours is the limit of endurance ; this event occurred in the case of a harpooned Whale. Fam. 2. Delphinidae.—This family, which includes the greater number of Cetacea, may thus be characterised:—Whales of small to moderate size. Teeth as a rule numerous, and present in the upper as well as in the lower jaw. Maxillae without large crests ; the pterygoids, often meeting in the middle line, enclose an air space open behind. The anterior (five to eight) ribs are two headed, the posterior with tubercular head only. The sternal ribs are ossified. The Dolphins and Porpoises, as already stated, embrace the greater number of existing species of "Whales. Sir W. Flower and others who have followed him, allow nineteen genera. But as to the exact number of known species there is much uncertainty. That very careful observer, Mr. True, considers2 that there are fifty which demand recognition. As many as one hundred have received names. The matter is one which is perhaps barely ripe for decision. All the Dolphin tribe are, for Whales, smallish animals. The Killer Whale, Orea, is the only genus (or species ?) which usually attains to more than moderate bulk. The rather mysterious Delphinus coronatus, 36 feet in length, of M. de ITre- minville, would seem to be a Ziphioid; it was described as having a very pointed beak, and as having the dorsal fin situated near the tail; such .characters suggest a Mesoplodon. The genus Delphinapterus, the Beluga or White Whale, con- sists of but a single species, though as usual more than one name has been given to supposed different species. It is char- acterised as a genus by the following assemblage of structural features:—It has only eight to ten teeth occupying the anterior part of the jaws only. All the cervical vertebrae are free and unjoined. The vertebral formula is O 7, B 11 (or 12), I/ 0, Ca 23. The pterygoids are wide apart, though, they converge as if about to meet at their posterior ends. There is no dorsal fin* The colour is white, 1 Prvc. ZooL Soc, 1882, pp. 722, 726. 2 &utt, U.8. JNat. Mwt. Ho. 86, 1889, p. 7.